In order to sustain the physiological well being of aircraft pilots required to breath oxygen and/or oxygen enriched air over long periods of time, recently developed aircraft breathing systems are equipped with hypoxia warning devices.
The most successful type of hypoxia warning device devised to date includes a polographic oxygen sensor. The polographic oxygen sensor continually monitors the partial pressure of oxygen in the breathable fluid supplied to the mask of the aircraft pilot. Should the oxygen level in the mask, as represented by the partial pressure, fall below a predetermined level, an alarm or indicator is activated to alert the pilot of a potential dangerous malfunction that could cause hypoxic conditions. Such polographic oxygen sensors provide a satisfactory warning for breathing systems in unpressurized aircraft cabins as long as the aircraft is below 28,000 feet in altitude. Unfortunately, in the event of decompression of the aircraft cabin above about 30,000 feet in altitude, the polographic oxygen sensor produces a warning signal due to a reduced total pressure even though the breathable fluid being supplied at that altitude is adequate.